406 GENERAL BIOLOGY 



have been a time when they did come into existence. The physico- 

 mechanists say, that while no living matter comes from non-living to- 

 day, yet, as there must have been a time when it did, we must assume 

 that different conditions once held sway from those we now know. 



But, such being the case, we break the most important law known 

 to science that of continuity. It is for this reason that it has been said, 

 that the breaking of this law of continuity is the only heresy known to 

 evolutionary science. 



The theory that life always comes from life is known as biogenesis, 

 while the theory which holds that life can come from non-living matter 

 is called abiogenesis. 



It will be noted that the evolutionary theories so far discussed have 

 only taken the physical side of the individual into consideration to the 

 entire neglect of the mental and intellectual. 



It was Alfred Russel Wallace, co-founder of the Natural Selection 

 theory with Darwin, who saw this quite early, and insisted that the 

 psychical or mental side must also be considered if we are to form truly 

 valid conclusions. He contended that once mentality enters, as it does in 

 man, such an organism could use this mentality to set aside or change 

 the physical selection which Nature carried on. In other words, the 

 earlier evolutionists were interested in the structure of nerves and nerve 

 elements, while Wallace saw the necessity of taking the thought which 

 is carried by the higher nerve centers ifito consideration. 



It is well for the student to know both the evidence adduced in sup- 

 port of evolution and evolutionary theories, and the objections which 

 have been hurled against it. We have, therefore, sutnnied up the argu- 

 ments of both sides, whether such support and objections are always con- 

 clusive or not. 



EVIDENCES FOR EVOLUTION 



1 . Paleontological. 



(a) There are many new kinds of plants and animals found in each 

 successive strata as shown by their fossil remains. 



(b) The later organisms are more complex than earlier ones. 



(c) The more recent fossils prove that they are quite closely re- 

 lated to the modern forms now living. 



2. Genetics. 



Breeding experiments as well as observation prove that all organ- 

 isms are constantly varying, and that constant variations in the same 

 group of organisms are transmitted to succeeding generations. 



3. Comparative Anatomy. 



The similarity of structure in different individuals is precisely what 

 would be experienced if evolution did take place. 



